The present invention generally relates to processing a semiconductor substrate. In particular, the present invention relates to a system and method of rinsing and draining a semiconductor substrate to mitigate pattern collapse.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions on semiconductor wafers (e.g., at submicron levels). In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes and the surface geometry such as corners and edges of various features. However, although the pattern width is reduced, the height of the pattern cannot be reduced very much. Thus, the aspect ratio (height/width) of the pattern increases and the pattern easily collapses.
Such patterns are formed in high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist and an exposing source (such as optical light, x-rays, etc.) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
The developing process involves exposing the irradiated wafer to the developer solution and then rinsing the developer solution from the wafer. Because the wafer still contains moisture and/or solution droplets on it, the wafer must be dried so that the rinsing solution can evaporate from the surface. However, at some point during the development process, the resist pattern has a tendency to collapse. More specifically, pattern collapse often occurs during the drying process, particularly when the rinsing solution begins to evaporate from the wafer surface.
FIGS. 1-4 illustrate an example of pattern collapse during a photolithography process. A substrate 10 is shown with patterns 20 provided thereon. It is noted that the patterns 20 are greatly exaggerated for ease of illustration. In FIG. 1, the substrate 10 is shown completely immersed in a developer liquid 30, which is enclosed within a processing chamber 25. The collapse of resist patterns 20 is more likely to occur after the substrate 10 has been developed and rinsed. In particular, resist pattern deformity may occur when the rinsing solution 30 begins to evaporate 35, as shown in FIG. 2. According to FIG. 2, the surface tension of the developer solution 30 remains between the resist patterns 20, causing resist pattern deformity 40.
FIG. 3 shows the substrate 10 as it appears during the drying process. As the surface of the substrate 10 continues to the dry, adjacent resist patterns 40 may lean toward and eventually against each other. The collapsed patterns 40 adversely affect the substrate 10 (or any other underlying layer) when an etching process 50 is conducted in or on the substrate 10. The deformed pattern eventually results in a deformed and defective substrate 60 (FIG. 4), thereby destroying the structurally integrity of the semiconductor device.
Therefore, there is an unmet need for a process to mitigate the collapse of resist patterns during the drying stage of a photolithography process.
The present invention provides an apparatus and a method for mitigating pattern collapse in a semiconductor substrate during the drying stage of a photolithography process. More specifically, the present invention involves the addition of hexane to the rinsing solution, thereby leaving hexane instead of water on the surface of the developed wafer. By employing a water-bexane rinsing solution, the surface tension is reduced between the developer solution and the resist. As a result, pattern collapse can be prevented, providing a more efficient and economical semiconductor manufacturing process.
One aspect of the present invention provides a semiconductor processing apparatus for rinsing a developed wafer to mitigate pattern collapse. The apparatus includes a bath chamber; a substrate holder disposed in the bath chamber for holding a substrate having a resist pattern formed thereon; a first nozzle for dispensing a first rinsing solution having a first density and first surface tension into the bath chamber; a second nozzle for dispensing a second rinsing solution having a second density and second surface tension, which is less than the first rinsing solution, into the bath chamber; a drain disposed in a bottom portion of the bath chamber; and a controlling system operatively coupled to the first nozzle, the second nozzle and the drain designed to regulate and coordinate the operation of the first nozzle, the second nozzle and the drain.
Yet another aspect of the present invention provides a method for rinsing a substrate during development to mitigate pattern collapse. The method involves the steps providing the substrate having a resist pattern transferred thereon into a bath chamber; exposing the substrate to a developer solution; removing the developer solution from the chamber via a drain; introducing a first rinsing solution into the bath chamber concurrently with removing the developer solution so that the substrate is immersed in liquid at substantially all times; removing the first rinsing solution from the chamber via the drain; introducing a hexane solution into the bath chamber concurrently with removing the first rinsing solution so that the substrate is immersed in liquid at substantially all times; and removing the hexane solution via the drain in order to dry the substrate.
Still yet another aspect of the present invention provides a method for rinsing a substrate during development to mitigate pattern collapse. The method involves the steps of providing the substrate having a resist pattern transferred thereon into a bath chamber; exposing the substrate to a developer solution; removing the developer solution from the chamber via a drain; introducing a water solution into the bath chamber concurrently with removing the developer solution so that the substrate is immersed in liquid at substantially all times, wherein the water solution rinses the developer solution from the substrate; removing the water solution from the chamber via the drain; introducing a hexane solution into the bath chamber concurrently with removing the water solution so that the substrate is immersed in liquid at substantially all times, wherein the hexane solution facilitates a subsequent drying process; and removing the hexane solution via the drain in order to dry the substrate.
To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.